Metallurgy of tin



Patented F eb. 17, 1925.

ELIAS ANTHON CAPPELEN SMITH, OF NEW YORK, N. Y.

METALLURGY OF TIN.

2N0 Drawing.

' To all whom it may concern:

Be it known that I, ELIAS ANTHoN CAP- PELEN SMITH, a citizen of the United States, residing at New York city, in the county of New York, State of New. York, have invented certain new and useful Ifmprovements in Metallurgy of Tin; and I do hereby declare the following to be a full, clear, and exactdescription of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

"This invention relates to the recovery of tin from ores and other tin-containing materials. More particularly the invention relates to a process of recovering tin from materials with which it is mixed and from which it cannot be separated readily by ordinarymetallurgical treatment. It is especially applicable to the treatment of low grade tin ores but may be employed also in treating higher grade ores and various materials containing tin or tin compounds.

The smelting of tin ores in ordinary shaft or reverberatory furnaces is not accomplished with the ease which characterizes the separation of copper or lead from ores containing these elements. The higher oxide of tin (SnO is not dissociated readily into the lower oxide (SnO) and oxygen by h'eat'alone at the temperatures-usual- 1y prevailing in the furnace. Consequently the distribution of oxygen is not easily accomplished, and special precautions are necessary to ensure eifective smelting. Thus in reverberatory smelting only the surface of the charge receivesienough oxygen for proper combustion of the carbonaceous reducing agent, and it is necessary to rabble the charge constantly so that fresh' material is brought to the surface 1n con-.

tact with the oxygen. There is a tendency, moreover, for the charge to fuse at the temperature at which carbon monoxide is pro:

duced (about 1 100C.), and fusion renders the charge less pervious and reduces the efficiency of the operation. This difiiculty' is met in shaft as well as in reverberatory furnaces. In either practice the first slag contains generally 20 to 40 per cent of tin, owing to inability of the oxygen to permeate the charge and to the tendency of the tin Application filed January 16, 1923. Serial No. 613,052.

ores. The application of the invention per-,

mits recovery of upward to 93 to 95 per cent of the tm in ores containing 5 to '6 per cent of tin.

In general the process depends upon the preliminary treatment of the ore or other material at temperatures much lower than those employed in ordinary smelting to brln the tin into a condition in which it is readlly soluble in solvents from which. it may be separated by electrolysis. /This prel minary treatment may be omitted if the tin is already in soluble form. Such treatment may include roasting, although this is not necessary with many tin-bearing materia ls. The ore or tin-bearing material,

either with or without previous roasting, is

crushed to a suitable degree of fineness (e. g., 20 mesh) and treated to bring the tin into soluble condition, for example, by reduct1on with a gaseous reducing agent or by sulphldizing. Reduction may be accompllshed by heating the material to about 800 C. to 850 C. with any suitable gas such as hydrogen, water gas, or gases produced from coal, oil or other fuel. Sulphidizing may be-carried out by conducting sulphur vapor from a convenient source into contact with the heated ore. These operations are continuedfor appropriate periods to ensure the accomplishment of the desired result.

When the tin content of the ore or material has beenbrought to the state in which it is soluble ,(if it is not naturally in that state) the material is leached with a solvent. Such a solvent may be a dilute sulphuric acid solution (e. g., 150 grams I-I SO per liter) containin 10 to 20 grams per liter of tin as stannic su phate and 10 to 50 grams per liter of iron, chiefly as ferric sulphate. During the leaching the stannic tin and ferric iron are largely reduced. to stannous tin and ferrous iron, and metallic tin is dissolved. The sulphuric acid dissolves a portion of the tin.

The tin-containing solution may be electrolyzed, using a lead anode and an ordinary current density of 10 to 20 amperes per square foot. Sheet tin forms a suitablecathode. As the tin is deposited on the cathode the. solvent is regenerated by the'oxidation of the tin and iron compounds, and the solution may be returned for the treatment of further quantities of tin-bearing materials, The solvent may be used repeatedly in this way until it accumulates a proportion of iron whichrenders it ineffective. All of the tin is then separated and the iron-contaiigling acid must be replaced with fresh aci This difiiculty is avoided by the use of a solvent containing a soluble polysulphide, for example, an alkali metal polysulphide, which selectively dissolves tin without taking up iron from the tin-containing material. A suitable solvent contains .100 grams of sodium sulphide and 30 grams of sulphur per liter. The solvent is regenerated by electrolyzing to deposit the tin. Lead or iron anodes may be employed with a current density of about 30 amperes per square foot at a temperature of C. to 60 C. The solvent may contain to grams of tin per liter before electrolysis, and 10 to 20 grams of tin per'liter when it is returned for reuse in leaching the tin-bearing material.

The soluble polysulphide solvent is particularly useful inconnection with the sulphidizing of the tin. The tin, instead of being reduced to the metallic state, is converted into the filtphide which is soluble readily in the sodi polysulphide solution. Under certain conditions where sulphur is cheaply available and fuel is expensive, the process described is particularly eficient and desirable. p

Soluble hydroxides, for example, alkali metal hydroxides, may also be used as a solvent for the treatment of material in which the tin has been reduced to the metallic condition. The tin is-less readily separated from the hydroxideso'lution, and a mixture of sodium hydroxide and sodium polysulphide is more desirable, the hydrox- I -ide serving to neutralize any tendency of the polysulphide to become acidic after repeated use. Soluble hydroxides, sulphides,

' polysulphides or mixtures of these are suitable solvents.

The most effective gaseous reducing agent for the practice of the invention is hydro-- gen whichvmay be obtained from any suitable source, by electrolysis of water, for example. Many gases containing hydrogen, carbon monoxide or hydrocarbons or mixtures thereof may be used in place of hydrogen. Thus, tomention a few available gases, water gas, producer gas, illuminating gas, oil gas or hydrocarbonvapors may be employed.

For the proper conduct of the reducing or sulphidizing operations suitable apparatus mustbe provided. In reducing iron furnaces or retorts may be used at the relatively low temperatures employed. It may be desirable, however, to use retorts, or furnaces be employed in carrying out the electrolysis.

of iron lined with refractory material such as magnesite or with a corrosion-resistant material such as an alloy of iron and chro- I mium containing not less than 30 per cent of chromium. Such alloys may contain upward to 60 per cent of chromium, and the entire furnace or retort, or any part thereof, may be constructed of this material. Alloys of iron with other elements such as titanium, uranium, vanadium and manga- F nese may also be employed in furnaces and retorts suitable for the purpose of the invention.

Electrolytic cells of the usual types may These' cells ma be equipped with diaphragms or not, depending upon special conditions affecting the operation. The cells and otherapparatus used, being .of wellknown construction, are not a part of the invention and are not described.

These and other details of the operation may vary, the specific examples being illustrative merely and are not intended as indicating the limits of the invention. Such variations are within the spirit of the invention and the scope of the accompanying claims.

I claim 1. The process of recovering tin from low grade tin-bearing material which comprises subjecting the material to the action of a gaseous reducing agent whereby the compounds of tin in the material are reduced, dissolving the tin in the thus-treated materialby means of an appropriate solvent, and recovering tin from the resulting solution by electrodeposition.

2. The process of recovering tin from tinbearing material, which comprises subjecting the material to the action of a gaseous reducing agent whereby the compounds of tin in the material are reduced, dissolving, the tin in the thus-treated material by means of an appropriate solvent, recovering. tin 11o frond the resulting solution by eleotrodeposition, and returning the spent electrolyte for the solution of further. tin from similarly treated tin-bearing material.

3. The process of recovering tin from tin-'- similarly treated bearing material.

5. The process of recovering tin from tinbearing material, which comprises subjecting the material ,to the action of a reducing gas, dissolving the tin with a solvent which is capable of regeneration by electrolytic treatment to deposit tin therefrom, and electrolyzing the solution to separate the tin.

6. The process of recovering tin from tinbearing material, which comprises subjecting the material to the action of sulphur vapors, dissolving the tin with a solvent which is capable of regeneration by electrolytic treatment to deposit tin therefrom, and electrolyzing the solution to separate a the tin.

7. The process of recovering tin from tinbearing material, which comprises subjecting the material to a preliminary treatment for rendering the tin content of the material more amenable to solution in an appropriate solvent capable of regeneration by the electrodeposition of tin therefrom,

dissolving the tin in the thus-treated ma-- 9. The process of recovering tin from tinbearing material, which comprises subject ing the material to the action of a gaseous reducing a ent whereby the compounds of tin are r uced, dissolving the tin in the thus-treated material by means of an appropriate solvent solution containing a soluble polysulfide, and recovering tin from the resulting solution by electrodeposition.

10. The process of recovering tin from tin-bearing material, which comprises subjecting the material to preliminary treatment for rendering the tin content thereof more amenable to solution in a solvent containing a soluble polysulfide, dissolving the tin in the thus-treated material by means of a solvent solution containing a soluble olysulfide, recovering tin from the resultmg solution by electrodeposition, and returnin the spent electrolyte for the solution of further tin from similarly treated tin-bearing material.

11. The process of recovering tin from tin-bearing material, which comprises subjecting the material at an elevated temperature to the action of a gaseous reducing agent, dissolving the tin in the thus-treated material by means of a solvent solution containing a soluble polysulfide, and recovering tin from the resulting solution by electrodeposition.

In testimony whereof I afiix my signature.

ELIAS ANTHON CAPPELEN SMITH. 

